1. Field of the Invention
The present invention relates to disk separator plates for reducing airborne noise and vibration in hard disk drives, and more particularly, pertains to methods of manufacturing disk separator plates.
2. Description of Related Art
It has been common practice for hard disk drives (HDD) to incorporate disk separator plates in order to reduce vibration caused by wind created by the rotating disk surfaces. This generates undesired noise in the hard disk drive assembly. It is thought that the disk separator plates should cover a maximum of the disk surfaces in order to minimize these vibration effects. It has been experimentally proven that the main airflow in a hard disk drive assembly, which is tangential to the circumferential edge of the rotating disks causes vortexes to be created between the airflow fluid layers, causing disk flutter and vibration of the magnetic reading heads during operation, thereby increasing noise and decreasing HDD performance.
The use of disk separator plates in hard disk drives has become common place. This increased use of disk separator plates in a hard disk drive increases the cost of the disk drive because of the increased raw materials required, and the secondary manufacturing operations required to make the disk separator plates, after initial stamping, forging, extrusion or casting.
FIG. 1 illustrates the environment in which disk separator plates of the present invention, also known as air damper plates, disk dampers, and anti disks, are utilized in a hard disk drive 9 which has a housing 11 with side walls 15 and 13 and a top enclosing the housing (not shown).
Contained within the housing 11 is the actuator drive assembly 17. An actuator 19, along with actuator arms 21 that carry read/write heads (22) are part of the drive assembly. A disk separator plate 25 is mounted over a top disk 23 to the side walls 15 and 13, or in any other convenient manner, to the housing 11 of hard disk drive 9. Besides being mounted over a disk stack 23, the disk separator plates are mounted between each of the disks in the disk stack, as will be explained hereinafter.
The shape and construction of the disk separator plates in the prior art are quite varied, although they have a common purpose of reducing airflow induced vibration.
FIG. 2 illustrates a disk separator plate 27 which is manufactured by casting and then machining to provide the correct thickness and flatness of the offset structures 31, 29, 32, and 33 which are used to hold the disk separator plate to the housing of a hard disk drive. Pins 30 and 34 are inserted into the casting or are machined from the casting as secondary operations. These pins mate with corresponding holes in the next separator plate in the stack, or in the drive base.
FIG. 3 illustrates a disk separator plate 35 that is manufactured by injection molding a plastic material. The plastic separator plate 35 has offset structures 37, 38 and 39 formed in the molding process.
FIG. 4 shows a disk separator plate 41 which is manufactured by extrusion and then milled or turned to reduce the main disk separator plate thickness 44 and establish the offset structures 42, 45, 46 required for mounting the disk separator plate to the housing of a hard disk drive. Boss 43 is milled from the extrusion to provide location alignment by nesting with an opposing separator plate or a drive base.
Each of these manufacturing processes has considerable shortcomings with respect to cost for the manufacturing methods used to produce metal disk separator plates. Furthermore, the ability to produce separator plates to precise dimensional control is difficult for each of the above described methods of manufacture.
The plastic injection molding process has special problems associated with it. The method produces voids and anisotropies in the product. The plastic plates are distorted when clamped. The plates are not as clean as required. The surface finish is not as smooth as required.
The major problem with the metal disk separator plates is the cost of manufacturing such plates.
FIG. 5 illustrates a side cross-section of a stack of disk separator plates 49, 51, 53, which are fastened to the enclosure 47 of a hard disk drive by a hold down bolt 55. The stack of disk separator plates illustrated is designed to cover the portions of the disks not swept by the use of the recording heads (not shown) which would rotate in the space between disk separator 49 and 51, 51 and 53, and 53 and the base 54 of housing 47. Hub 57 is the center around which the disks rotate.
The offsets 56, which are designed to provide the correct amount of separation between the disk separators 49, 51, and 53, and the base 54 of the hard disk drive are created as part of the separator plate during the manufacturing process. As can be seen by the structure of the offset 56 of separator plate 49, for example, the machining required after initial manufacturing is significant and increases the cost of each separator plate. The amount of metal required to make forged, fully machined, or extruded and machined disk separator plates is large because the starting thickness is at least that of the full offset height. The main plate thickness of the separator plate must be created by removing material.
Although flat stamped disk separator plates provide the best dimensional control, of all these manufacturing processes, at a minimum manufacturing cost, the stamping process cannot create the thickness, or material reduction required in a typical offset at the mounting points for the disk separator plate.
Accordingly, the present invention provides a method for manufacturing disk separator plates using disk stamping techniques which reduce raw material content and secondary manufacturing operations, while providing the necessary offset heights, required at the offset points, used for mounting the separator plates to the hard disk drive.